1. Field of the Invention
The present invention relates to a toner supply device, and more particularly to a toner supply device for supplying toner from a toner container located apart from a developing device to the developing device.
2. Background Information
An image forming device utilizing an electrophotographic system includes a photosensitive drum as an image bearing member and other devices located circumferentially around the drum, such as a charger, an exposure device, a developing device, a transfer device, a cleaning device, and so on. In addition, a fixing device is provided downstream of the photosensitive drum in a direction in which the transfer device extends. In this image forming device, first, a surface of the photosensitive drum is uniformly charged by the charger. Then, the photosensitive drum is exposed by the exposure device in accordance with image data so that an electrostatic latent image is formed on the photosensitive drum. The electrostatic latent image is developed by the developing device. In a case of the full color image forming device, four developing units are provided for storing cyan developer, magenta developer, yellow developer, and black developer. The developing units develop the latent image to a toner image with four colors (cyan, magenta, yellow, and black). After that, the toner image is transferred to a transfer medium by the transfer device and then fixed to the transfer medium by the fixing device, and the transfer medium is finally discharged to a discharge unit. Residual developer remaining on the photosensitive drum is cleaned by the cleaning device.
In the above-mentioned image forming operation, the toner in the toner container is consumed as the development is carried out so that it is necessary to refill the toner. There are two systems to compensate for the toner consumed by the image forming operation.
The first system is to fill a certain amount of the toner in the developing unit and replace the developing units when the toner is completely consumed, as shown in Japanese Unexamined Patent Publication No. 2004-45960. In this system, the developing unit and the toner container are formed into a cartridge, so that it is not necessary to supply the toner to the developing unit. Consequently, it is easy to maintain the developing unit.
The second system is to provide a toner container outside of the developing unit so as to supply the toner to the developing unit from outside, as shown in Japanese Unexamined Patent Publications No. 2001-134045 and No. 10-198149. Recently, as full color image forming devices have been increasingly used by individuals, there have been demands to reduce the size of the image forming device. It is necessary to reduce the size of the developing units in order to reduce the size of the image forming device. In the second system, by providing the toner container outside of the developing unit, the developing unit will be reduced in size.
In the first system wherein the developing unit and the toner container are formed into a cartridge, it is necessary to fill the toner for about 4,000 sheet printing in the developing unit in advance because the toner is not supplied to the developing unit from outside. As a result, it is difficult to reduce the developing unit in size. Although it is possible to set a printing capability of toner to 4,000 sheets or under, the cost per one sheet increases in that case. In addition, when the toner is completely consumed, it is necessary to replace the developing units each time. As a result, it increases the burden on the environment.
On the contrary, in the system wherein the toner container is provided outside of the developing unit and the toner is supplied to the developing unit from outside, it is necessary to prepare a member for supplying the toner from the toner container to the developing unit. For example, a plurality of toner supply paths are provided for supplying the toner to each of the developing units in the device shown in Japanese Unexamined Patent Publication No. 2001-134045, and a plurality of toner supply pipes are provided for supplying the toner to each of the developing units in the device shown in Japanese Unexamined Patent Publication No. 10-198149. The toner is supplied to the developing units through the toner supply paths or the toner supply pipes from the toner container.
However, in the conventional devices, the toner may remain in the toner supply paths or the toner supply pipes. In particular, in the device shown in Japanese Unexamined Patent Publication No. 10-198149, the toner supply pipes advance and retreat relative to the developing units, so that when the toner supply pipe leaves the developing unit, the toner remaining in the toner supply pipes scatter about so as to contaminate inside of the device.
Furthermore, in the conventional device, it is difficult to precisely manage the amount of the toner supply when the toner is supplied from the toner container to the developing unit, because the toner in the toner container is supplied to the developing device by free fall.
It is an object of the present invention to restrain the toner from remaining in the toner supply unit and from contaminating the inside of the device when the toner is supplied to the developing unit from the toner container located apart from the developing unit.
It is another object of the present invention to precisely manage the amount of the toner supply to the developing unit with a simple structure.